Re: Who is causing all this i/o?

On 5/20/11 4:25 PM, Scott Marlowe wrote:
> On Fri, May 20, 2011 at 3:14 PM, Craig James<craig_james(at)emolecules(dot)com> wrote:
>> Our development server (PG 8.4.4 on Ubuntu server) is constantly doing
>> something, and I can't figure out what. The two production servers, which
>> are essentially identical, don't show these symptoms. In a nutshell, it's
>> showing 10K blocks per second of data going out, all the time, and
>> essentially zero blocks per second of input.
>> After a lot of digging around, I found this in the /postgres/pg_stat_tmp
>> directory. If I list the directory including the i-nodes once every second,
>> I find that a new 2MB file is being created roughly once every two seconds:
> Have you got a lot of databases in your development environment? I
> think that can sometimes cause a lot of pg_stat writes.
Yes. The production servers have a dozen or so databases, but the development server has a couple hundred databases. Does that count as "a lot of databases"?

We've had even more databases in the past (>500) and didn't see this sort of I/O activity.

The odd thing is that this activity is gradually growing, so slowly that you don't notice it right away. A month or two ago, nothing. A couple weeks ago, a constant stream of "grass" in xload's graph. Today, xload is showing a 50% all the time. I can only guess that the load will continue to increase.

Is there a way to tell Postgres not to do this, or to do it less? It's not a big disaster (yet), but it's annoying to have the system spewing a couple megabytes of pg_stat_tmp data every few seconds.

Thanks,
Craig